Blockchain needs to be a trust-less network where you can rely on storing value transfers safely. Leading zeroes on every block are achieved by iterating a nonce value, that ensures immutability because there is no other way to get the right hashes without re-doing all proof of work to find it. You cannot rely on a regular database because on a decentralized peer to peer network, someone would be able to alter some data on its own benefit breaking the trustless system